1. Field of the Invention
This invention relates to a new moisture-hardening coating compositions containing organic polyisocyanates as binders and to a process for their preparation.
2. Description of the Prior Art
Moisture-hardening coating compositions containing organic polyisocyanates, particularly NCO prepolymers of relatively high molecular weight, as the binder are known (cf. for example H. Kittel, Lehrbuch der Lacke und Beschichtungen, 1973, Verlag W. A. Colomb, Vol. I, Part 2, pages 573-576).
The quality of the paint films obtained from such coating compositions and, in particular, the stability of the ready-to-use coating compositions in storage are critically determined by the dryness of the auxiliaries and additives, such as pigments, fillers and/or solvents. Accordingly, these additives have to be satisfactorily dried before production of the coating compositions. Highly reactive, organic isocyanates have been successfully used for this drying (DE-PS 1 245 590, DE-OS 2 539 728 and DE-OS 3 204 128).
However, the use of such highly reactive, low molecular weight isocyanate compounds, in particular tosyl isocyanate, is also attended by disadvantages including high vapor pressure; often extremely high reactivity, which necessitates particular precautionary measures; and, especially, the fact that the isocyanates react with water to form insoluble secondary products, such as ureas, which crystallize out of the paint mixture, cause clouding and can thus lead to film defects and poor levelling.
Accordingly, an object of the present invention is to provide new coating compositions based on isocyanate compounds which do not involve the use of highly reactive isocyanates as drying agents, but which nevertheless show excellent stability in storage in the absence of moisture and lead to high-quality paint films.
This object was achieved in accordance with the present invention as described in detail hereinafter.